Carbon Balance and Metabolic Changes of Kentucky Bluegrass in Responses to Elevated Temperature and Carbon Dioxide Concentration.

Elevated CO₂ concentration has been found to mitigate the adverse effects of increasing temperatures in various plant species, including cool-season grass species.  The objective of this study was to investigate metabolic factors associated with the interactive effects of elevated CO₂ and increasing temperatures on cool-season turfgrass species.  Kentucky bluegrass (cv. ‘Baron’) plants were grown in growth chambers with ambient CO₂ (400 ppm) and elevated CO₂ (800 ppm) and day/night temperature treatments of 15/12, 20/17, 25/22, 30/27, 35/32 ^oC under well-watered conditions.  Increasing temperatures at and above 25 ^oC resulted in significant decline in turf quality.  Plants at elevated CO₂ consistently had significantly higher turf quality at all temperature regimes than those at ambient CO₂.  Single-leaf photosynthesis (Pn) decreased while respiration rate (R) increased with increasing temperatures and respiration rate exceeded Pn at and above 25 ^oC.  Elevated CO₂ significantly suppressed the increases in respiration rate, particularly at 30/27 and 35/32 ^oC, and resulted in higher Pn/R ratio.  The content of soluble sugars (i.e. glucose and sucrose) and organic acids (i.e. citric acid and oxalic acid) decreased with increasing temperatures above 20/17 ^oC under both ambient and elevated CO₂.  Elevated CO₂ treatment mitigated the decline in the content of those soluble sugars and amino acids under high temperatures. Elevated CO₂ also increased the accmulation of animo acids (i.e. alanine, serine, aspartic acid, and threonine) under different temperature regimes. The results suggested that the positive effects of elevated CO₂ could be assocaited with the maintenance of carbon balance and accumulation of key metabolites regulating plant growth.